1. Field of the Invention
The present invention relates to an optical element and an optical scanning device using the element and, more particularly, to a scanning optical device which records image information by reflecting/deflecting a light beam emitted from a light source means using a deflection means, and optically scanning a scanning target surface via an imaging optical system and is suitable for an apparatus using an electrophotographic process, such as a laser beam printer or digital copying machine.
2. Related Background Art
Conventionally, in an optical scanning device used for a laser printer or the like, a light beam which is optically modulated in accordance with an image signal and emitted from a light source means is periodically deflected by a deflection means formed by, for example, a polygon mirror, and the light is focused into a spot on a photosensitive recording medium surface (photosensitive drum surface) by the second imaging optical system having an f-xcex8 characteristic, thereby optically scanning the surface and recording image information.
FIG. 23 is a schematic view of the main part of a conventional optical scanning device.
Referring to FIG. 23, a divergent light beam emitted from a light source means 91 is converted into a substantially parallel light beam by a condenser lens (collimator lens) 82. The light beam width is limited by an aperture stop 83 and incident on a cylindrical lens 92. Of the substantially parallel light beam incident on the cylindrical lens 92, the light in a main scanning cross-section emerges without any change. The light in a sub scanning cross-section converges and is substantially formed into a linear image on a deflection/reflection surface 93a of a deflection means 93 comprising by a polygon mirror. The light beam reflected/deflected by the deflection/reflection surface 93a of the polygon mirror 93 is guided onto a recording medium surface (scanning target surface) 97 via a second imaging optical system 95 constituted by f-xcex8 lenses 95a and 95b having an f-xcex8 characteristic and a return mirror 96. By rotating the polygon mirror 93 by a driving means 94 at a substantially equiangular velocity, the recording medium surface 97 which is a photosensitive drum is optically scanned at a substantially constant speed. With this operation, a latent image based on a potential difference is formed.
The above f-xcex8 lenses 95a and 95b are accurately positioned with respect to the optical path of a light beam reflected/deflected by the polygon mirror 93 and fixed on an optical frame (not shown) by a known method, e.g., bonding or spring pressure. For example, Japanese Laid-Open Patent Application Nos. 9-73038 and 9-329755 disclose a case where an f-xcex8 lens is accurately positioned by bringing a positioning reference on the incident surface side of the f-xcex8 lens into contact with a positioning member of an optical frame.
Japanese Patent No. 3004064 discloses a case where the incident and exit surfaces of an f-xcex8 lens are simultaneously positioned by bringing the incident surface into contact with a incident-surface-side positioning member and bringing the exit surface into contact with an exit-surface-side positioning member. This prevents curvature of field on a recording medium surface or a deterioration in uniformity (f-xcex8 characteristic) of scanning speed.
Japanese Laid-Open Patent Application No. 7-113973 discloses a case where focus adjustment on a recording medium surface is performed by mounting an f-xcex8 lens on a moving means and moving it in the optical axis direction. In addition, a cylindrical lens is moved in the optical axis direction to set a spot diameter on a recording medium surface in the sub scanning direction to a desired value. At this position, the lens is fixed on an optical frame by a known method, e.g., bonding or spring pressure, thereby performing focus adjustment in the sub scanning direction.
Recently, there have been increasing demands for an increase in the resolution of an optical scanning device and a decrease in cost. With an increase in resolution, optical elements such as an f-xcex8 lens and cylindrical lens need adjustment. For this purpose, new parts are required, and the adjustment time prolongs, resulting in an increase in adjustment cost.
It is an object of the present invention to provide an optical element which can reduce an assembly cost by simplifying focus adjustment of the optical element, decreasing the number of parts required for the adjustment, and shortening the adjustment time, and an optical scanning device using the element.
In one aspect of the invention, an optical element comprises a plurality of sets of positioning references for defining a position in an optical axis direction and said plurality of sets of positioning references define different positions in the optical axis direction.
In further aspect of the foregoing optical element, said positioning references of each set are formed on opposing surfaces.
In further aspect of the foregoing optical element, said positioning reference is formed into a stepped shape.
In further aspect of the foregoing optical element, said optical element has a focusing effect in one direction.
In another aspect of the invention, an optical scanning device comprises light source means, a first imaging optical system which focuses a light beam emitted from said light source means, deflection means for causing a deflection/reflection surface to reflect/deflect a light beam passing through said first imaging optical system to deflect the light beam as a deflected light beam at an equiangular velocity, and a second imaging optical system which optically scans the deflected light beam on a scanning target surface and forms the light beam into an image as a spot on the scanning target surface, and at least one of optical elements included in said first and second imaging optical systems has a plurality of sets of positioning references for defining a position of said optical element in the optical axis direction.
In further aspect of the foregoing optical scanning device, said positioning references of said optical element are formed on front and rear surfaces in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element has a projection portion on an outer portion formed outside an effective portion, and surfaces of the projection portion which is located on front and rear sides in the optical axis direction form the positioning references.
In further aspect of the foregoing optical scanning device, an optical frame which houses said first imaging optical system or/and said second imaging optical system has a plurality of sets of positioning portions corresponding to the positioning references of said optical element, and an interval between the positioning portions of said optical frame in the optical axis direction of said optical element is larger than an interval between the positioning references of said optical element in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element has a recess portion in an outer portion formed outside an effective portion, and surfaces of said recess portion which are located on front and rear sides in the optical direction form the positioning references.
In further aspect of the foregoing optical scanning device, an optical frame which houses said first imaging optical system or/and said second imaging optical system has a plurality of sets of positioning portions corresponding to the positioning references of said optical element, and an interval between the positioning portions of said optical frame in the optical axis direction of said optical element is smaller than an interval between the positioning references of said optical element in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element is positioned to a position where one of said plurality of sets of positioning references for defining a position of said optical element in the optical axis direction is in contact with one of said plurality of positioning portions of said optical frame or a position where one of said plurality of sets of positioning references is not in contact with the positioning portions of said optical frame.
In further aspect of the foregoing optical scanning device, said optical element is placed between said plurality of sets of positioning portions of said optical frame.
In further aspect of the foregoing optical scanning device, the positioning reference also serves as a contact surface of a positioning tool.
In further aspect of the foregoing optical scanning device, said optical element is made of a synthetic resin material.
In further aspect of the foregoing optical scanning device, said optical element has a plurality of sets of positioning references, each constituted by two reference surfaces that define said optical element at the same position in the optical axis direction.
In further aspect of the foregoing optical scanning device, said optical element has a focusing effect only in one of a main scanning direction and a sub scanning direction.
In further aspect of the foregoing optical scanning device, said optical element has a focusing effect only in one of the main scanning direction and the sub scanning direction, and a positioning reference of said optical element is formed into a stepped shape in a direction in which said optical element has no focusing effect.
In still another aspect of the invention, an optical scanning device comprises light source means, a first imaging optical system which focuses a light beam emitted from said light source means, deflection means for causing a deflection/reflection surface to reflect/deflect a light beam passing through said first imaging optical system to deflect the light beam as a deflected light beam at an equiangular velocity, and a second imaging optical system which optically scans the deflected light beam on a scanning target surface and forms the light beam into an image as a spot on the scanning target surface, wherein one of lenses constituting said first and second imaging optical systems has, on light incident and exit surfaces of said lens, positioning references for defining a position of said lens in the optical axis direction.
In further aspect of the foregoing optical scanning device, the device further comprises an optical frame which houses said first imaging optical system or/and said second imaging optical system, and said optical frame has positioning portions corresponding to the positioning references of said lens on front and rear sides in a direction of an optical axis of said lens, and an interval between the positioning portions of said optical frame in the direction of the optical axis of said lens is larger than an interval between the positioning references of said lens in the optical axis direction.
In further aspect of the foregoing optical scanning device, said lens is positioned such that the positioning reference which is formed on a light incident surface side of said lens and defines a position in the direction of the optical axis of said lens is in contact with the positioning portion of said optical frame on the light incident surface side, positioned such that the positioning reference which is formed on the light exit surface side and defines a position in the direction of the optical axis of said lens is in contact with the positioning portion of said optical frame on the light exit surface side, or positioned between the positioning portions on the light incident and exit surface sides without contacting the positioning portions of said optical frame.
In further aspect of the foregoing optical scanning device, said lens is made of a synthetic resin material.
In further aspect of the foregoing optical scanning device, said lens comprises, on the light incident and exit surface sides of said lens, two pairs of positioning references for defining a position in the direction of the optical axis of said lens.
In further aspect of the foregoing optical scanning device, said lens has a focusing effect only in one of the main scanning direction and the sub scanning direction.
In further aspect of the foregoing optical scanning device, said lens is formed by a composite lens obtained by integrating a cylindrical lens having a focusing effect only in the sub scanning direction and a synchronous detection lens which guides a light beam to synchronous detection means, and the positioning reference positions said composite lens in a direction parallel to the direction of the optical axis of the synchronous detection lens of said composite lens.
In still another aspect of the invention, an image forming apparatus comprises the foregoing optical scanning device, a photosensitive member placed on the scanning target surface, a developing unit which develops an electrostatic latent image formed on said photosensitive member by a light beam scanned by said optical scanning device into a toner image, a transfer unit which transfers the developed toner image onto a transfer material, and a fixing unit which fixes the transferred toner image on the transfer material.
In still another aspect of the invention, an image forming apparatus comprises the foregoing optical scanning device, and a printer controller which converts code data input from an external device into an image signal and inputs the signal to said optical scanning device.